For retailers everywhere, the rules of engagement have changed. As smartphones, tablets and other mobile device proliferate, shopping has evolved from a discrete activity into a continuous and always-on process. Today, buying a product can happen at any time and anywhere, and it’s never more than an arm’s length away.

To make the most of this new reality, retailers must take a more active role in the customer journey and guide shoppers through each step of the process. The most effective way to do this is by creating a multi-channel messaging strategy, one that addresses specific customers needs, provides valuable content and nudges shoppers toward purchase.

Let’s examine five ways that leading retailers use mobile messaging to boost their sales:

1. Always make shopping top-of-mind.
During the discovery phase of shopping, people are browsing for ideas, reading reviews and collecting inspiration on social media sites like Pinterest. While they are not actively looking to buy, they are open to the idea if it’s presented in the right context.

Email is a particularly good messaging channel to get people into the shopping mindset. Banana Republic sends a mobile-optimized email newsletter each week with new product announcements, sales and other promotions. This regular outreach informs potential customers about the company's latest happenings and keeps the brand top-of-mind. Retailers with apps can also use an in-app news feed to drive consideration via smart editorial content, new product announcements and seasonal promotions.

2. Create opportunities through context.
In the subsequent phase of the shopping process, people commit to making a purchase. For online retailers, this means directing them to an ecommerce site or mobile app when a transaction will take place.

Push notifications are an excellent marketing channel to achieve this goal, as they give retailers direct access to their audience, wherever they may be. Fashion companies like Gilt and RueLaLa have perfected this type of messaging by sending time-sensitive announcements ("Our sale is starting now!') at a specific times during the day, typically during lunchtime and evenings.

For brick-and-mortar retailers, the challenge is a little more difficult as they need to drive people into a physical store. In this situation, push notifications are also effective when paired with a shopper’s location data. For example, Walgreens uses push notifications to alert app users about their prescriptions when in close proximity of a retail location. Another option is to send mobile coupons via email for in-store redemption, a strategy used by retailers like Bed Bath & Beyond.

3. Make the experience easy and interactive.
Getting people comfortable in a shopping environment requires the right mix of digital tools, personal reassurance and competitive products. Together, these elements build a retailer’s value proposition to the customer.

WalMart enhances its shopping experience with a mobile app that has a special "store mode," giving customers quick access to their shopping lists, detailed product information and a bar code scanner for faster checkout. App features aside, retailers can also use in-app messaging to proactively welcome customers who enter a store, educate them about different shopping resources or promote featured items. Some retailers are also experimenting with in-app customer support to answer questions that arise while shopping.

4. Remind customers to buy.
Once shoppers have selected items to buy, they still need a nudge to complete their purchase. Using push notifications and email is a powerful way for retailers to remind people to transact. Online retailer Asos minimizes shopping cart abandonment via an automatically triggered email sent 30 minutes after an item has been added to its cart (provided a purchase has not yet been made). Some retailers also offer last-minute coupons to create an additional incentive to buy.

5. Keep an open dialogue post-purchase.
Extending the shopping experience post-purchase in another big opportunity for retailers to engage their audience.

Simple transactional emails like purchase confirmations and shipping updates are great for managing customer expectations. Amazon recently made these updates more accessible on-the-go by offering them via push notifications. Social sharing, the most popular activity on mobile devices, is perfect for brand evangelism and referral traffic. Online retailer Fab asks customers to share their purchase on Facebook and Twitter immediately after the transaction. Mobile surveys, on the other hand, are an effective way to gauge customer satisfaction, and can be triggered via push notifications one or two days post-purchase.

As mobile makes shopping more complex and unpredictable, retailers require a new set of tools to stay relevant. Multi-channel mobile messaging is the most effective way for them to inform and enhance the shopping experience. By communicating with their customers in the right place at the right time, not only will retailers create an engaging dialogue -- they will also build a predictable path to purchase.